I have been REPOSTING nearly 100% of my content (with original credits/attribution etc. from the original poster). Guess what? Across 5 different IG accounts, I only got ONE complaint from the original poster to remove their photo. Everyone else? THANKS FOR THE REPOST!, Please follow me, etc.
As long as you are giving proper credit for the reposts, most people "get it" that you are actually promoting THEIR IG accounts via yours - which is true, and I like that about IG.
On a separate & interesting note.... It would appear by the number of likes & comments these reposts are getting... most people don't bother reading/noticing it's a repost - they seem to think they are my original photos?!?!?! Not sure what that means about IG users, but it's probably not good if you're trying to activate/engage/motivate (and sell) them.